1. Field of the Invention
The present invention relates to a technique in a memory for storing data used directly by a user (user data), which is intended to reduce capacity of a reserve storage region which does not directly store the user data.
2. Description of the Background Art
In memories, generally, logical addresses and physical addresses are directly brought into correspondence with each other since defective blocks are admitted. Therefore, as to memories, it is conventionally well known that reserve storage regions are provided to store information required for conversion between logical addresses and physical addresses.
As a method therefor, a reserve region is provided correspondingly to each data region (block) serving as a unit of access, to store characteristics information indicating whether the block is normal or defective therein. Then, at a predetermined timing (e.g., at power-on), a controller reads the characteristics information from all the reverse regions to make a table on the correspondence between logical addresses and physical addresses. Alternatively, such a table is held in the memory.
(Patent Document 1) Japanese Patent Application Laid Open Gazette No. 10-049447.
Though the characteristics information indicating whether each block is normal or defective is a small piece of information, however, if the information on all the blocks are stored, a rather large reserve region is needed since the number of blocks is very large.
Further, if an accessed block happens to be defective, another block may be retrieved. In this case, however, the access speed is different depending on whether the block is normal or defective, and therefore the access speed that can be assured is reduced.